Oxide sintered body and sputtering target

ABSTRACT

An oxide sintered body having metal elements composed of In, Ga, Zn and Sn and containing a hexagonal layered compound represented by InGaO3(ZnO)m (m is an integer of 1 to 6). When ratios (atomic %) of contents of In, Zn and Sn to all metal elements excluding oxygen contained in the oxide sintered body are taken as [In], [Zn] and [Sn], respectively, the relations [Zn]≥40 atomic %, [In]≤15 atomic %, [Sn]≤4 atomic % are satisfied.

TECHNICAL FIELD

The present invention relates to an oxide sintered body and a sputteringtarget, which are used when an oxide semiconductor thin film of athin-film transistor (TFT) for use in a display device such as liquidcrystal display and organic EL display is deposited by a sputteringmethod.

BACKGROUND ART

An amorphous (non crystalline) oxide semiconductor for use in TFT has ahigh carrier mobility and a large optical band gap and can be depositedat a low temperature, compared with general-purpose amorphous silicon(a-Si). Therefore, its application to a next-generation displayrequiring large size, high resolution and high-speed drive and to aresin substrate having low heat resistance is expected. As a compositionof the oxide semiconductor suitable for these applications, anIn-containing amorphous oxide semiconductor has been proposed and, forexample, a product using an In—Ga—Zn-based oxide (IGZO) semiconductor isput into practical use. In addition, for the purpose of impartingdifferent properties such as high mobility, an Sn-containing oxidesemiconductor such as In—Ga—Zn—Sn-based oxide semiconductor andIn—Ga—Sn-based oxide semiconductor is attracting attention.

In forming the above-described oxide semiconductor thin film, asputtering method of subjecting a sputtering target (hereinaftersometimes referred to as “target material”) of the same material as thethin film to sputtering is suitably used. The sputtering target is usedin a state of an oxide sintered body being bonded to a backing plate,but the oxide sintered body is sometimes cracked in the process ofbonding the oxide sintered body to the backing plate.

In the Sn-containing oxide semiconductor above, a crystal phase derivedfrom Sn may be generated, but there is disclosed a technique forobtaining a good semiconductor film by controlling the crystal phase andthereby suppressing cracking of a sputtering target or suppressingabnormal electrical discharge during sputtering. For example, PatentLiteratures 1 and 2 disclose an In—Zn—Sn-based oxide semiconductorcontaining a hexagonal layered compound represented by In₂O₃(ZnO)_(m) (mis an integer of 3 to 9) and a spinel structure compound represented byZn₂SnO₄.

In addition, Patent Literature 3 discloses a technique where in the caseof an In—Ga—Zn—Sn-based oxide sintered body having added thereto Zn, inorder to prevent a compound represented by InGaO₃(ZnO)_(m) (m is aninteger of 1 to 20) as a main component of the IGZO-based oxide fromabnormally growing to bring about abnormal electrical discharge and inturn causing a defect in the obtained film, the contents of In, Ga, Znand Sn are adjusted, and any of Ga₂In₆Sn₂O₁₆, Ga_(2.4)In_(5.6)Sn₂O₁₆ and(Ga,In)₂O₃ is used as the main component.

CITATION LIST Patent Literature

Patent Literature 1: International Publication No. 2000/067571

Patent Literature 2: International Publication No. 2007/037191

Patent Literature 3: Japanese Patent No. 5,522,889

SUMMARY OF INVENTION Technical Problem

Meanwhile, in order to enhance the wet etching property (the solubilityof an oxide semiconductor thin film to an etching solution for oxidesemiconductor processing, such as oxalic acid) in an oxide semiconductorthin film of TFT using an In—Ga—Zn—Sn-based oxide sintered body, a largeamount of Zn needs to be added. However, a system in which a largeamount of Zn is added has a problem that the above-described compoundrepresented by InGaO₃(ZnO)_(m) is likely to abnormally grow and due tocoarsening of the grain size of the compound, the oxide sintered bodyis, in particular, readily cracked in the process of bonding theobtained oxide sintered body to a backing plate.

The present invention has been made under these circumstances, and anobject thereof is to provide an oxide sintered body capable ofsuppressing occurrence of cracking at the time of bonding even in anIn—Ga—Zn—Sn-based oxide sintered body in which a large amount of Zn isadded, and a sputtering target using the oxide sintered body.

Solution to Problem

As a result of many intensive studies, the present inventors have foundthat when an oxide sintered body used for a sputtering target has aspecific composition and crystal phases, the object above can beattained, and have accomplished the present invention.

That is, the present invention includes the following [1].

[1] An oxide sintered body having metal elements composed of In, Ga, Znand Sn and containing a hexagonal layered compound represented byInGaO₃(ZnO)_(m) (m is an integer of 1 to 6),

wherein when ratios (atomic %) of contents of In, Zn and Sn to all metalelements excluding oxygen contained in the oxide sintered body are takenas [In], [Zn] and [Sn], respectively, the following expressions (1) to(3) are satisfied:[Zn]≤40 atomic %  (1)[In]≤15 atomic %  (2)[Sn]≤4 atomic %  (3)

In addition, preferred embodiments of the present invention include thefollowing [2] to [6].

[2] The oxide sintered body according to [1] above, whereinInGaO₃(ZnO)_(m) includes hexagonal layered compounds represented byInGaO₃(ZnO)₃ and InGaZn₂O₅.

[3] The oxide sintered body according to [2] above, wherein when theoxide sintered body is subjected to X-ray diffraction, the InGaO₃(ZnO)₃and InGaZn₂O₅ satisfy the following expression (4):[InGaO₃(ZnO)₃]+[InGaZn₂O₅]≥0.9  (4),

wherein[InGaO₃(ZnO)₃]=I(InGaO₃(ZnO)₃)/(I(InGaO₃(ZnO)₃)+I(InGaZn₂O₅)+I(Ga₂In₆Sn₂O₁₆)+I(Ga₃InSn₅O₁₆)+I(Zn₂SnO₄))and[InGaZn₂O₅]=I(InGaZn₂O₅)/(I(InGaO₃(ZnO)₃)+I(InGaZn₂O₅)+I(Ga₂In₆Sn₂O₁₆)+I(Ga₃InSn₅O₁₆)+I(Zn₂SnO₄));

in the expression, I(InGaO₃(ZnO)₃), I(InGaZn₂O₅), I(Ga₂In₆Sn₂O₁₆),I(Ga₃InSn₅O₁₆) and I(Zn₂SnO₄) are respectively diffraction peakintensities of InGaO₃(ZnO)₃ phase, InGaZn₂O₅ phase, Ga₂In₆Sn₂O₁₆ phase,Ga₃InSn₅O₁₆ phase and Zn₂SnO₄ phase identified by X-ray diffraction.

[4] The oxide sintered body according to any one of [1] to [3] above,wherein the average grain size of the oxide sintered body is 10 μm orless.

[5] The oxide sintered body according to [4] above, wherein an averagegrain size is 6 μm or less.

[6] A sputtering target obtained by using the oxide sintered bodyaccording to any one of [1] to [5] above, which has a resistivity of 1Ω·cm or less.

Advantageous Effects of Invention

According to the present invention, an oxide sintered body capable ofsuppressing occurrence of cracking at the time of bonding even in anIn—Ga—Zn—Sn-based oxide sintered body in which a large amount of Zn isadded, and a sputtering target using the oxide sintered body can beprovided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph (X-ray diffraction chart) illustrating the X-raydiffraction results of the oxide sintered body of the present inventionin Example 2.

FIG. 2 is a diagram illustrating EPMA test results (element mapping) ofthe oxide sintered body of the present invention in Example 2.

DESCRIPTION OF EMBODIMENTS

The present inventors have made intensive studies on an oxide sinteredbody so as to provide an oxide sintered body for sputtering targets,which enables stable deposition over a long period of time by thesuppression of abnormal electrical discharge during sputtering andcracking of a sputtering target material and moreover, is suitable fordepositing an oxide semiconductor film capable of enhancing wet etchingproperty.

As a result, it has been found that in an oxide sintered body havingmetal elements composed of In, Ga, Zn and Sn, when each of the contentsof respective metal elements contained in the oxide sintered body isappropriately controlled, an oxide sintered body composed ofpredetermined crystal phases can be obtained and cracking of the oxidesintered body can be suppressed while ensuring excellent wet etchingproperty.

Specifically, it has been found out that (a) when a large amount (40atomic % or more) of Zn is added, excellent wet etching property can beensured; and (b) when not more than a predetermined amount (15 atomic %or less) of In is added and not more than a predetermined amount (4atomic % or less) of Sn is added, fine crystal phases composed of acompound of InGaO₃(ZnO)_(m) (m is an integer of 1 to 6) in which Sn isuniformly solid-dissolved are formed while suppressing generation ofSn-derived crystal phases such as Ga₂In₆Sn₂O₁₆, Ga₃InSn₅O₁₆ and Zn₂SnO₄and a structure resistant to bonding cracking is obtained. The presentinvention has been accomplished based on this finding.

First, the oxide sintered body according to the present invention isdescribed in detail.

The oxide sintered body of the present invention has metal elementscomposed of In, Ga, Zn and Sn and contains a hexagonal layered compoundrepresented by InGaO₃(ZnO)_(m) (m is an integer of 1 to 6), wherein whenratios (atomic %) of contents of In, Zn and Sn to all metal elementsexcluding oxygen contained in the oxide sintered body are taken as [In],[Zn] and [Sn], respectively, the following expressions (1) to (3) aresatisfied:[Zn]≥40 atomic %  (1)[In]≤15 atomic %  (2)[Sn]≤4 atomic %  (3)

Here, in order to form an oxide sintered body having excellent wetetching property and capable of suppressing cracking of the oxidesintered body in the bonding process, each of the contents of respectivemetal elements contained in the oxide sintered body needs to beappropriately controlled.

Specifically, when the ratios (atomic %) of the contents of In, Zn andSn to all metal elements excluding oxygen contained in the oxidesintered body are taken as [In], [Zn] and [Sn], respectively, the ratiosare controlled to satisfy the following expressions (1) to (3):[Zn]≥40 atomic %  (1)[In]≤15 atomic %  (2)[Sn]≤4 atomic %  (3)

Expression (1) defines the Zn ratio ([Zn]=Zn/(In+Ga+Zn+Sn)) in all metalelements. Zn has a function of enhancing amorphization of the oxidesemiconductor thin film.

If [Zn] is too low, the effect of enhancing the wet etching property ishardly obtained. Accordingly, [Zn] is 40 atomic % or more, preferably 45atomic % or more, more preferably 50 atomic % or more, still morepreferably 55 atomic % or more.

In addition, if [Zn] is too high, it is likely that the content of Inrelatively decreases, causing a reduction in the field-effect mobility,or the content of Ga relatively decreases, causing a reduction in theelectrical stability of the oxide semiconductor thin film. Accordingly,[Zn] is preferably 65 atomic % or less, more preferably 60 atomic % orless.

Expression (2) defines the In ratio ([In]=In/(In+Ga+Zn+Sn)) in all metalelements. In general, In is an element contributing to enhancement ofthe electrical conductivity.

If [In] is too high, formation of a crystal phase having a bixbyitestructure, such as In₂O₃, or an Sn-containing crystal phase such asGa₂In₆Sn₂O₁₆, tends to be induced. As a result, cracks develop startingfrom such a crystal phase and can give rise to a cause of cracking atthe time of bonding. Accordingly, [In] is 15 atomic % or less,preferably 12 atomic % or less, more preferably 10 atomic % or less.

In addition, if [In] is too low, the field-effect mobility may decrease.Accordingly, [In] is 1 atomic % or more, preferably 3 atomic % or more,more preferably 7 atomic % or more.

Expression (3) defines the Sn ratio ([Sn]=Sn/(In+Ga+Zn+Sn)) in all metalelements. In general, Sn has a function of enhancing the chemicalresistance of the oxide semiconductor thin film, such as wet etchingproperty.

If [Sn] is too high, generation of Sn-derived crystal phases (a crystalphase such as Ga₂In₆Sn₂O₁₆, Ga₃InSn₅O₁₆ or Zn₂SnO₄) cannot besuppressed. As a result, cracks develop starting from the crystal phasegenerated and can give rise to a cause of cracking at the time ofbonding. Accordingly, [Sn] is 4 atomic % or less, preferably 3.5 atomic% or less, more preferably 3 atomic % or less.

In addition, if [Sn] is too low, although details are described later, astate of Sn being uniformly solid-dissolved in the compound ofInGaO₃(ZnO)_(m) (m is an integer of 1 to 6) contained in the oxidesintered body according to the present invention is not created, and theeffect of suppressing growth of the crystal phase by the pinning effectof the solid-dissolved Sn is hardly obtained. Accordingly, [Sn] is 1atomic % or more, preferably 1.5 atomic % or more, more preferably 2atomic % or more.

Next, the hexagonal layered compounds represented by InGaO₃(ZnO)_(m) (mis an integer of 1 to 6) detected when the oxide sintered body accordingto the present invention is subjected to X-ray diffraction aredescribed. More specifically, the hexagonal layered compounds arehexagonal layered compounds represented by InGaO₃(ZnO)₃ and InGaZn₂O₅.

Each of InGaO₃(ZnO)₃ and InGaZn₂O₅ is an oxide formed by bonding of In,Ga and Zn and O constituting the oxide sintered body of the presentinvention. Unlike the above-described crystal phase such asGa₂In₆Sn₂O₁₆, Ga₃InSn₅O₁₆ or Zn₂SnO₄, Sn contained in the oxide sinteredbody does not constitute the skeleton of a crystal structure but isuniformly solid-dissolved in the crystal phase of InGaO₃(ZnO)₃ orInGaZn₂O₅.

Whether Sn is uniformly solid-dissolved in the crystal phase above canbe confirmed by the X-ray diffraction results and in-plane compositionmapping using EPMA (Electron Probe X-ray Micro Analyzer, electron probemicroanalysis).

As described above, when Sn is uniformly solid-dissolved in thesecrystal phases, the solid-dissolved Sn can fulfill the so-called pinningrole against coarsening of each crystal phase. Accordingly, if Sn itselfconstitutes the skeleton of a crystal phase as in Ga₂In₆Sn₂O₁₆,Ga₃InSn₅O₁₆ or Zn₂SnO₄, this is disadvantageous in that the pinningeffect cannot be effectively produced. In order for Sn not to constitutethe skeleton of a crystal phase and to be uniformly solid-dissolved inthe crystal phase, as described above, it is important to add not morethan a predetermined amount of Sn.

By virtue of the pinning effect due to Sn, the average grain size of thehexagonal layered compounds such as InGaO₃(ZnO)₃ and InGaZn₂O₅ can bekept small, and the effect of suppressing cracking at the time ofbonding can be enhanced.

Furthermore, in order to more enhance the effect of preventing crackingat the time of bonding, it is preferable to refine the average grainsize of grains of the oxide sintered body. Specifically, the averagegrain size of grains observed with a scanning electron microscope (SEM)in a fracture surface (an arbitrary position on a section surface whenthe oxide sintered body is cut at an arbitrary position in the thicknessdirection) of the oxide sintered body is controlled to preferably 10 μmor less, and cracking of the oxide sintered body can thereby be moreprevented.

The average grain size of grains of the oxide sintered body is morepreferably 8 μm or less, still more preferably 6 μm or less, yet stillmore preferably 5 μm or less. On the other hand, the lower limit valueof the average grain size is not particularly limited, but in view ofthe balance between refining of the average grain size and productioncost, the lower limit of the average grain size is preferably about 0.05μm.

Furthermore, in the present invention, it is preferable to appropriatelycontrol the grain size distribution as well as the average grain size ofgrains of the oxide sintered body. Specifically, coarse grains having agrain size exceeding 15 μm give rise to cracking of the oxide sinteredbody at the time of bonding and therefore, the proportion thereof ispreferably as small as possible. Accordingly, the area ratio of coarsegrains having a grain size exceeding 15 μm in the entire grains ispreferably 10% or less, more preferably 8% or less, still morepreferably 6% or less, yet still more preferably 4% or less.

The relative density of the oxide sintered body of the present inventionis preferably 90% or more. By increasing the relative density of theoxide sintered body, the effect of preventing cracking at the time ofbonding can be more enhanced. The relative density of the oxide sinteredbody of the present invention is more preferably 95% or more, still morepreferably 98% or more. The upper limit value is not particularlylimited and may be, for example, 100%, but in view of production cost,the upper limit is preferably 99%.

In order to further enhance the effect of suppressing cracking at thetime of bonding, it is preferred that the diffraction peak intensitiesof InGaO₃(ZnO)₃ phase and InGaZn₂O₅ phase identified by X-raydiffraction satisfy the following expression (4):[InGaO₃(ZnO)₃]+[InGaZn₂O₅]≥0.9  (4)wherein[InGaO₃(ZnO)₃]=I(InGaO₃(ZnO)₃)/(I(InGaO₃(ZnO)₃)+I(InGaZn₂O₅)+I(Ga₂In₆Sn₂O₁₆)+I(Ga₃InSn₅O₁₆)+I(Zn₂SnO₄))and[InGaZn₂O₅]=I(InGaZn₂O₅)/(I(InGaO₃(ZnO)₃)+I(InGaZn₂O₅)+I(Ga₂In₆Sn₂O₁₆)+I(Ga₃InSn₅O₁₆)+I(Zn₂SnO₄)).

In the expression, I(InGaO₃(ZnO)₃), I(InGaZn₂O₅), I(Ga₂In₆Sn₂O₁₆),I(Ga₃InSn₅O₁₆) and I(Zn₂SnO₄) are respectively diffraction peakintensities of InGaO₃(ZnO)₃ phase, InGaZn₂O₅ phase, Ga₂In₆Sn₂O₁₆ phase,Ga₃InSn₅O₁₆ phase and Zn₂SnO₄ phase identified by X-ray diffraction.Incidentally, “I” means that it is the measured value of X-raydiffraction intensity (diffraction peak intensity).

With respect to diffraction peaks obtained by subjecting the oxidesintered body to X-ray diffraction, the compound phases of InGaO₃(ZnO)₃and InGaZn₂O₅ have crystal structures described in ICSD (InorganicCrystal Structure Database) cards 00-064-0801 and 00-040-0252,respectively (corresponding to InGaO₃(ZnO)₃ phase and InGaZn₂O₅ phase,respectively) (see Table 2).

In the present invention, when the oxide sintered body is subjected toX-ray diffraction, it is preferred that the total of InGaO₃(ZnO)₃ phaseand InGaZn₂O₅ phase is contained in a predetermined ratio.

When the diffraction peak intensity ratios of InGaO₃(ZnO)₃ phase andInGaZn₂O₅ phase are decreased, this means that in the entire oxidesintered body, the proportion of InGaO₃(ZnO)₃ phase and InGaZn₂O₅ phasecontributing to the suppression of coarsening of grains by virtue ofpinning effect of Sn decreases and consequently, the proportion ofprecipitated crystal phases (e.g., Ga₂In₆Sn₂O₁₆, Ga₃InSn₅O₁₆, Zn₂SnO₄)other than these compounds increases.

In this case, cracks develop starting from crystal phases other thanInGaO₃(ZnO)₃ phase and InGaZn₂O₅ phase, which are locally precipitated,and may give rise to a cause of cracking at the time of bonding. Forthis reason, [InGaO₃(ZnO)₃]+[InGaZn₂O₅] is preferably 0.9 or more, morepreferably 0.95 or more, still more preferably 0.99 or more.

A suitable production method for the oxide sintered body of the presentinvention is described below.

The oxide sintered body of the present invention is obtained by mixingand sintering indium oxide; gallium oxide; zinc oxide; and tin oxide,and the sputtering target can be produced by processing the oxidesintered body. Specifically, the sputtering target can be obtained bysubjecting oxide powders to (a) mixing/pulverization→(b)drying/granulation→(c) preforming→(d) degreasing→(e) atmosphericsintering, and subjecting the obtained oxide sintered body to (f)processing→(g) bonding.

Of these steps, in the present invention, as described in detail below,it may be sufficient if the selection conditions of indium oxide,gallium oxide, zinc oxide and tin oxide as raw material powders and theconditions of atmospheric sintering ((e)) are appropriately controlled.Other steps are not particularly limited, and usually employed steps maybe appropriately selected. In the following, each step is described, butthe present invention is by no means limited thereto.

First, an indium oxide powder; a gallium oxide powder; a zinc oxidepowder; and a tin oxide powder are blended in a predetermined ratio,followed by mixing and pulverization. Each of the raw material powdersused preferably has a purity of about 99.99% or more because an impurityelement, if present in a trace amount, may impair semiconductingproperties of the oxide semiconductor thin film. The blending ratio ofrespective raw material powders is preferably controlled such that theratios of contents of indium, gallium, zinc and tin to all metalelements excluding oxygen contained in the oxide sintered body fallwithin the ranges above.

The (a) mixing/pulverization is preferably performed using a ball millby charging the raw material powders thereinto together with water. Asthe ball or bead used in this step, a ball or bead formed of, forexample, materials such as nylon, alumina and zirconia is preferablyused. On this occasion, a dispersant for the purpose of homogeneousmixing, and a binder for ensuring ease of the subsequent forming step,may be mixed.

Next, a mixed powder obtained in the step above is preferably subjectedto the (b) drying/granulation by means of, for example, a spray drier.

After drying/granulation, the (c) preforming is performed. In performingthe forming, the powder after drying/granulation fills a die having apredetermined dimension and is preformed by die pressing. The preformingis performed for the purpose of enhancing the handling property at thetime of setting in a sintering furnace and therefore, is sufficient if acompact is formed by applying a pressure of approximately from 0.5 to1.0 tonf/cm².

Thereafter, forming (main forming) is performed by CIP (Cold IsostaticPressing). For increasing the relative density of the oxide sinteredbody, the pressure during forming is preferably controlled to about 1tonf/cm² or more.

In the case where a dispersant or a binder is added to the mixed powder,it is preferable to perform the (d) degreasing by heating the compact soas to remove the dispersant or binder. The heating conditions are notparticularly limited as long as the purpose of degreasing can beachieved, but, for example, the compact may be kept in the air generallyat about 500° C. for about 5 hours.

After degreasing, the compact is set in a die providing a desired shapeand sintered by (e) atmospheric sintering.

In the present invention, sintering is performed at a sinteringtemperature: from 1,300 to 1,600° C., for a holding time at thistemperature: from 1 to 50 hours. In addition, it is preferable to oncehold the compact at 1,100 to 1,300° C. for 1 to 10 hours. By selectingthese temperature ranges and holding times, compound phases satisfyingexpressions (1) to (3) can be obtained.

If the sintering temperature is low, the compact cannot be sufficientlydensified, and the material strength decreases. On the other hand, ifthe sintering temperature is too high, the grain is coarsened, making itimpossible to control the average grain size of grains to apredetermined range, and the material strength decreases. Accordingly, asintering temperature is 1,300° C. or more, preferably 1,350° C. ormore, more preferably 1,400° C. or more, and 1,600° C. or less,preferably 1,550° C. or less.

In the present invention, the average temperature rise rate up to thesintering temperature above after forming is preferably 100° C./hr orless. If the average temperature rise rate exceeds 100° C./hr, abnormalgrowth of grain is likely to occur, and the relative density cannot besufficiently increased.

In the sintering step, the sintering atmosphere is preferably set to anoxygen gas atmosphere (for example, air atmosphere) or an oxygen gaspressurized atmosphere. The pressure of the atmosphere gas is preferablyset to an atmospheric pressure so as to suppress evaporation of zincoxide having a high vapor pressure.

After an oxide sintered body is obtained as above, (f) processing (g)bonding are performed in a conventional manner, as a result, thesputtering target of the present invention is obtained. The processingmethod for the oxide sintered body is not particularly limited, and theoxide sintered body may be processed into a shape according to varioususes by a known method.

The sputtering target can be obtained by bonding the processed oxidesintered body to a backing plate by use of a bonding material. The typeof the material of the backing plate is not particularly limited, butpure copper or copper alloy having excellent thermal conductivity ispreferred. The type of the bonding material is also not particularlylimited, and various known bonding materials having electricalconductivity can be used. Examples thereof include an In-based soldermaterial and an Sn-based solder material.

The bonding method is also not particularly limited and may be, forexample, a method in which the oxide sintered body and the backing plateare melted by heating at a temperature causing melting of the bondingmaterial, for example, at approximately from 140 to 220° C., the moltenbonding material is applied to the bonding surface of the backing plate,respective bonding surfaces are stuck together, and both arepressure-bonded and then cooled.

In the sputtering target obtained using the oxide sintered body of thepresent invention, cracking due to a stress, etc. developed by shock,heat history, etc. during the bonding operation does not occur. Theresistivity is also very good and is preferably 1 Ω·cm or less, morepreferably 10⁻¹ Ω·cm or less, still more preferably 10⁻² Ω·cm or less.

When the sputtering target of the present invention is used, depositionin which the abnormal electrical discharge during sputtering and thecracking of the sputtering target material are more suppressed can beachieved, and physical vapor deposition (sputtering method) using thesputtering target can be efficiently performed in the production line ofa display device. In addition, the oxide semiconductor thin filmobtained also exhibits good TFT properties.

EXAMPLES

The present invention is more specifically described below by referringto Examples and Comparative Examples, but the present invention is notlimited to the following Examples and can also be implemented by makingchanges within the range conformable to the gist, and all of thesechanges are encompassed by the technical scope of the present invention.

(Preparation of Sputtering Target)

An indium oxide powder (In₂O₃) having a purity of 99.99%, a zinc oxidepowder (ZnO) having a purity of 99.99%, a gallium oxide powder (Ga₂O₃)having a purity of 99.99% and a tin oxide powder (SnO₂) having a purityof 99.99% were blended at a ratio shown in Table 1, and water and adispersant (ammonium polycarboxylate) were added thereto, followed bymixing in a zirconia ball mill for 24 hours. Then, the mixed powderobtained in the step above was dried and granulated.

The thus-obtained powder was preformed by die pressing (formingpressure: 1.0 tonf/cm², size of compact: ϕ110×t 13 mm, t is thethickness) and then subjected to main forming at a forming pressure of3.0 tonf/cm² by CIP (cold isostatic pressing).

The compact obtained in this way was allowed to rise in temperature to500° C. at normal pressure in an air atmosphere and held at thattemperature for 5 hours to effect degreasing. The compact afterdegreasing was set in a sintering furnace and sintered.

The resulting sintered body was machined to a finished dimension ofϕ100×t5 mm and bonded to a Cu-made backing plate to prepare a sputteringtarget.

(Average Grain Size)

With respect to each of Examples and Comparative Examples, the “AverageGrain Size (μm)” in Table 1 was measured as follows.

First, the oxide sintered body was broken down, and its fracture surface(an arbitrary position on a section surface when the oxide sintered bodywas cut at an arbitrary position in the thickness direction) wasmirror-polished to prepare a sample. Next, a photograph of the structurethereof was taken at a magnification of 400 times by using a scanningelectron microscope (SEM); a straight line having a length of 100 μm wasdrawn in an arbitrary direction; the number (N) of grains includedwithin the straight line was determined; and the value calculated from[100/N] was taken as “grain size on straight line”. Similarly, 20straight lines were drawn at such intervals as keeping coarse grainsfrom overlapping with each other (at intervals of at least 20 μm ormore), and the grain sizes on individual straight lines were calculated.Then, the value calculated from [the sum of grain sizes on individualstraight lines/20] was taken as “average grain size of oxide sinteredbody”.

(Cracking at the Time of Bonding)

With respect to each of Examples and Comparative Examples, the presenceor absence of “Cracking at the Time of Bonding” in Table 1 was measuredas follows.

First, the sintered body was processed into a shape of 4 inches indiameter and 5 mm in thickness and bonded to a backing plate to obtain asputtering target. At this time, the sintered body and backing platewere allowed to rise in temperature on a hot plate up to 180° C. over 20minutes, and the bonding operation was performed using a wettingmaterial (In metal). After the bonding operation, whether or notcracking occurred on the oxide sintered body surface was confirmed withan eye. When a crack exceeding 1 mm was observed on the oxide sinteredbody surface, “cracking” was judged to be present. The bonding operationwas performed 10 times, and when cracking occurred even only once, thesample was evaluated as failed and indicated by “present” in Table 1. Onthe other hand, when cracking did not occur even once out of 10 times,the sample was evaluated as passed and indicated by “none” in Table 1.

(Peak Intensity Ratios of InGaO₃(ZnO)₃ Phase and InGaZn₂O₅ Phase)

With respect to each of Examples and Comparative Examples, the “PeakIntensity Ratios of InGaO₃(ZnO)₃ Phase and InGaZn₂O₅ Phase” in Table 1were measured as follows.

First, the sputtering target obtained by sputtering was removed from thebacking plate, and a test piece of 10 mm square was cut out therefromand subjected to the following X-ray diffraction to determine the X-raydiffraction pattern of each oxide sintered body. Analyzer: “X-rayDiffractometer RINT-TTR-III” manufactured by Rigaku Corporation

Analysis Conditions:

Target: Cu

Monochromatization: Use of monochromator (Kα)

Target output: 40 kV-200 mA

(Continuous Measurement) θ/2θ Scanning

Slits: Divergence: 1/2°, Scattering: 1/2°, Receiving: 0.15 mm

Monochromator receiving slit: 0.6 mm

Scanning speed: 2°/min

Sampling interval: 0.02°

Measurement angle (2θ): 5 to 90°

As an example, FIG. 1 shows a graph (X-ray diffraction chart)illustrating X-ray diffraction results for the oxide sintered body ofExample 2. From the thus-obtained X-ray diffraction chart of each oxidesintered body, respective compound phases (crystal phases) wereidentified based on the above-described ICSD cards and measured for thediffraction peak intensity (height of diffraction peak) shown in Table2.

As for the peak, among the compound phases, a peak having a highdiffraction peak intensity and having as little overlapping with thepeaks of other compound phases as possible was selected. The measuredvalues of the peak height at a designated peak in individual compoundphases are denoted respectively by I(InGaO₃(ZnO)₃), I(InGaZn₂O₅),I(Ga₂In₆Sn₂O₁₆), I(Ga₃InSn₅O₁₆) and I(Zn₂SnO₄) (wherein “I” means thatit is the measured value of X-ray diffraction intensity (diffractionpeak intensity)), and the total of the peak intensity ratio ofInGaO₃(ZnO)₃ phase and the peak intensity ratio of InGaZn₂O₅ phase,i.e., [InGaO₃(ZnO)₃]+[InGaZn₂O₅], was determined according to thefollowing expressions.[InGaO₃(ZnO)₃]=I(InGaO₃(ZnO)₃)/(I(InGaO₃(ZnO)₃)+I(InGaZn₂O₅)+I(Ga₂In₆Sn₂O₁₆)+I(Ga₃InSn₅O₁₆)+I(Zn₂SnO₄))[InGaZn₂O₅]=I(InGaZn₂O₅)/(I(InGaO₃(ZnO)₃)+I(InGaZn₂O₅)+I(Ga₂In₆Sn₂O₁₆)+I(Ga₃InSn₅O₁₆)+I(Zn₂SnO₄))

Peaks of compound phases other than those described above were hardlyobserved.

In this Example, when the thus-obtained [InGaO₃(ZnO)₃]+[InGaZn₂O₅] was0.9 or more, the sample was evaluated as passed.

(Confirmation that Sn is Uniformly Solid-Dissolved)

With respect to each of Examples, in order to confirm that Sn wasuniformly solid-dissolved in the crystal phase of InGaO₃(ZnO)₃ orInGaZn₂O₅, the oxide sintered bodies of Examples 1 to 6 were subjectedto element mapping of the Sn distribution by means of EPMA. Themeasurement conditions of EPMA are as follows:

Analyzer: “JXA-8900RL” manufactured by JEOL Ltd.

Analysis Conditions:

Accelerating voltage: 15.0 kV

Irradiation current: 1.998×10⁻⁸ Å

Beam diameter: minimum (0 μm)

Measurement time: 100.00 ms

Number of measurement points: 250×250

Measurement interval: X 0.40 μm, Y 0.40 μm

Measurement area: 400 μm×400 μm

Number of measurement visual fields: 1 visual field

As an example, FIG. 2 illustrates the results of element mapping for theoxide sintered body of Example 2. First, a color scale is depicted inright side of FIG. 2, and “CP” in the top-left photograph of FIG. 2means a reflected electron image. In addition, the oxide sintered bodycontains Zn and In as elements other than O (oxygen), Ga and Snillustrated in FIG. 2, but element mapping photographs thereof areomitted. Furthermore, in FIG. 2, assuming Level of Sn at a pointexhibiting a maximum Sn concentration is 500 and Level of Sn at a pointnot containing Sn is 20, the Sn concentration at each point is expressedby a relative value to the maximum concentration, i.e., Level: 500. And,the abundance ratio of each Level is denoted by the area ratio (Area %).

Referring to the results of Sn in FIG. 2, the area ratio of Level: 140or less is 100.0% (10.9+89.1=100.0%) in total, and it is seen that Sn isuniformly solid-dissolved in the crystal phase without causingsegregation.

It could be confirmed that similarly to the results of Example 2, thearea ratio of Level: 140 or less is 90% or more in total also inExamples other than Example 2. These could verify that the oxidesintered body according to the present invention constitutes crystalphases of InGaO₃(ZnO)₃ and InGaZn₂O₅ as revealed by the X-raydiffraction results above and Sn is uniformly solid-dissolved in thecrystal phase of InGaO₃(ZnO)₃ or InGaZn₂O₅ as revealed by the EPMAresults above.

TABLE 1 Aver- Crack- Peak Intensity Composition of Oxide age ing Ratiosof Sintered Body Grain at the InGaO₃(ZnO)₃ (atomic %) Size Time of and[In] [Ga] [Zn] [Sn] (μm) Bonding InGaZn₂O₅ Example 1 9.1 30.4 58.2 2.3 7none 0.994 Example 2 11.3 29.6 56.3 2.8 5 none 0.993 Example 3 14.0 26.756.3 3.0 5 none 0.995 Example 4 12.3 28.3 56.2 3.2 8 none 0.991 Example5 13.6 33.1 49.8 3.5 7 none 0.973 Example 6 10.2 29.6 56.4 3.8 9 none0.974 Compar- 16.7 38.7 40.2 4.4 15 present 0.752 ative Example 1Compar- 17.5 35.2 42.7 4.6 19 present 0.701 ative Example 2

TABLE 2 Reference ICSD Index of Peak Measured Crystal Phase Card No. (hk l) InGaO₃(ZnO)₃ 00-064-0801 (0 1 8) InGaZn₂O₅ 00-040-0252 (1 0 4)Ga₂In₆Sn₂O₁₆ 01-089-7011 (3 1 2) Ga₃InSn₅O₁₆ 00-051-0214 (−6 0 1)Zn₂SnO₄ 01-074-2184 (1 1 1)

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope of the invention. This applicationis based on Japanese Patent Application (Patent Application No.2017-099949) filed on May 19, 2017 and Patent Application (PatentApplication No. 2018-002052) filed on Jan. 10, 2018, the entirety ofwhich is incorporated herein by way of reference.

The invention claimed is:
 1. An oxide sintered body, comprising metalelements composed of In, Ga, Zn and Sn and comprising a hexagonallayered compound represented by InGaO₃(ZnO)_(m), wherein m is an integerof 1 to 6, and when ratios (atomic %) of contents of In, Zn and Sn toall metal elements excluding oxygen comprised in the oxide sintered bodyare taken as [In], [Zn] and [Sn], respectively, the followingexpressions (1) to (3) are satisfied:[Zn]≤40 atomic %  (1)[In]≤15 atomic %  (2)[Sn]≤4 atomic %  (3).
 2. The oxide sintered body of claim 1, whereinInGaO₃(ZnO)_(m) comprises hexagonal layered compounds represented byInGaO₃(ZnO)₃ and InGaZn₂O₅.
 3. The oxide sintered body of claim 2,wherein when the oxide sintered body is subjected to X-ray diffraction,the InGaO₃(ZnO)₃ and InGaZn₂O₅ satisfy the following expression (4):[InGaO₃(ZnO)₃]+[InGaZn₂O₅]≥0.9  (4) wherein[InGaO₃(ZnO)₃]=I(InGaO₃(ZnO)₃)/(I(InGaO₃(ZnO)₃)+I(InGaZn₂O₅)+I(Ga₂In₆Sn₂O₁₆)+I(Ga₃InSn₅O₁₆)+I(Zn₂SnO₄))and[InGaZn₂O₅]=I(InGaZn₂O₅)/(I(InGaO₃(ZnO)₃)+I(InGaZn₂O₅)+I(Ga₂In₆Sn₂O₁₆)+I(Ga₃InSn₅O₁₆)+I(Zn₂SnO₄)),wherein I(InGaO₃(ZnO)₃), I(InGaZn₂O₅), I(Ga₂In₆Sn₂O₁₆), I(Ga₃InSn₅O₁₆)and I(Zn₂SnO₄) are respectively diffraction peak intensities of anInGaO₃(ZnO)₃ phase, an InGaZn₂O₅ phase, a Ga₂In₆Sn₂O₁₆ phase, aGa₃InSn₅O₁₆ phase and a Zn₂SnO₄ phase identified by X-ray diffraction.4. The oxide sintered body of claim 1, wherein an average grain size ofthe oxide sintered body is 10 μm or less.
 5. The oxide sintered body ofclaim 4, wherein the average grain size is 6 μm or less.
 6. A sputteringtarget obtained by using the oxide sintered body of claim 1, wherein thesputtering target has a resistivity of 1 Ω·cm or less.